The process of toilet training children has received surprisingly little attention in the medical research literature, and many parents may welcome guidance from their physician on how best to carry out this important parental duty. Theory and prescription for toilet training in the United States since 1900 has traced a pendulum's path between the polar opposites of passive permissiveness and systematic control. Since midcentury, the trend in the United States has been toward delayed toilet-training, typically between the child's second and third year. Like all trends, however, this one may reverse. Given children's developmental differences, a new trend toward early toilet training, if it emerges, may be accompanied by an increase in toilet-training problems. If so, physicians who advise parents and treat pediatric populations may wish to become more familiar with data-based behavioral management of toilet training and the implications of this approach for early toilet training and the treatment of toileting-refusal behavior.